Rotary engines such as the ones known as Wankel engines use the eccentric rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor includes a number of apex portions which remain in contact with a peripheral wall of the rotor cavity of the engine throughout the rotational motion of the rotor.
The eccentric rotary motion of the rotor is guided through a rotor phasing gear which is meshed with a stator phasing gear, and at least one oil seal is provided around the phasing gear to prevent oil from entering the combustion area. Double oil seal rings with radially spaced seals are typically provided in each end face of the rotor for improved sealing. However the rotor must be sufficiently large to accommodate this double oil seal while leaving sufficient room for the gas seals located radially outwardly thereof.